In 2010, the number of smart mobile devices worldwide has exceeded 1.35 billion units. The manufacturing processes of these electronic products require more than 90% of manual assembling. In recent years, minimum wages for labors have significantly increased, which severely erodes the gross profit of the electronic components assembly industry. In addition, with an aging population and low birth rate, most countries also face the problem of the shortage of labors. In view of these, there is an ongoing demand for automated assembly technology to facilitate the assembly of the electronic components in order to overcome the above problems and also to address the increasing complexity in the characteristics of electronic products assembly, such as compliance characteristic required by operations like polishing or deburring.
Due to the requirements of the automated assembly technology as mentioned above, a substantial increase in investment for multi-axis mechanical arms has been seen in the electronic components assembly industry. Parallel mechanical arms, since having a lighter structure and a faster speed and being combined with visual feature recognition techniques, have a competitive advantage when applied to the assembly work of electronic components. As a result, the parallel mechanical arms are often used in the “odd-form” assembly, and are gradually replacing the horizontal multi-joint mechanical arms.
The parallel mechanical arms, when operating at a high speed, still have a vibration problem that needs to be overcome. If vibration can be overcome to reduce cycle time, production efficiency will be significantly increased and the mechanical arms can be applied to various technical field. Furthermore, with the development trend of modern electronic products that are required to be compact-sized and low-profiled and electronic substrates that are required to have multi-layered designs, various kinds of connectors become more difficult to be assembled. Although assembly lines have gradually become automated, ultimately, some electronic components still require manual assembly. This is mainly because the mechanical arms still lack the compliance as the manual operations.
A dual-drive joint mechanism that achieves both position and stiffness controls has been proposed. This mechanism includes a dual driving element and a planetary gear set. Its primary driving element is a low-speed and high-torque motor used for position control and its secondary driving element is a high-speed and low-torque motor used for stiffness modulation. The primary and the secondary driving elements drive a mechanical joint in series through the planetary gear set, and in turn a mechanical arm is driven. Position control and stiffness modulation of the mechanical arm are achieved by controlling the motor speeds.
However, the above prior-art technique still has backlash issues. Furthermore, the planetary gear set has a speed reduction ratio that requires careful selections of matching driving elements. Therefore, the design of the controller becomes less flexible.